The paper addresses the role of the mammalian pluripotency factor Nanog, in zebrafish. The role of Nanog in zebrafish is controversial. While some studies suggest that Nanog is a master embryonic regulator that initiates transcription during zygotic genome activation, other studies suggest that Nanog is only required to form an extraembryonic tissue called the yolk syncytial layer (YSL). In this paper, using a gene knockout and tissue-specific rescue experiments, Jamie & co demonstrate that Nanog is in fact primarily required for YSL formation.